Waste having high aluminum (Al) content in the form of coal ash or soil generated by construction work and the like has come to be used in large amounts as a cement clinker raw material from the viewpoint of effective utilization of waste. In general, since the amount of the aluminate phase (C3A) present in cement clinker increases with the amount of Al contained in the raw materials, the amounts of Al and C3A contained in cement clinker increase accompanying expanded utilization of waste containing large amounts of Al such as coal ash. Therefore, in order to obtain a suitably fresh properties (fluidity), it is necessary to increase the amount of water required for normal consistency of cement paste (amount of water for achieving a standard consistency of cement paste: amount of water required to obtain a fixed consistency) or the water content of concrete. On the other hand, when the amount of water required for normal consistency of cement paste or the water content of concrete is increased, there is concern over this increase having a detrimental effect on properties other than fresh properties such as strength development. Consequently, there is the problem of being forced to limit the amount of waste used to a fixed amount in order to not allow an increase in the amount of water required for normal consistency of cement paste or the water content of concrete.
Non-Patent Document 1 describes chemical analysis values for various types of Portland cement (normal Portland cement (N), high early strength Portland cement (H), moderate heat Portland cement (M) and low heat Portland cement (L)). The amounts of C3A are calculated from each component of the chemical analysis values (such as Al2O3 and Fe2O3) using the Bogue equation, and the amounts of water required for normal consistency of cement paste (amount of water for achieving a standard consistency of cement paste: amount of water required to obtain a fixed consistency) required for these amounts of C3A are shown in Table 1.
TABLE 1Amount of waterrequired forC3Anormalcalculatedconsistency ofAl2O3Fe2O3valuecement pasteType(%)(%)(%)(%)PortlandN (normal)5.152.808.927.9cementH (high early4.832.688.330.6strength)M (moderate3.874.073.427.1heat)L (low heat)2.662.552.727.4
As shown in Table 1, normal Portland cement (N) and high early strength Portland cement (H), which have high C3A contents, have higher amounts of water required for normal consistency of cement paste in comparison with moderate heat Portland cement (M) and low heat Portland cement (L).
Examples of methods used to improve the fluidity of mortar or concrete include “using an inorganic powder in the manner of limestone fine powder (Patent Document 1)”, “adjusting the form of the gypsum mixed in (Patent Document 2)”, and “using an aggregate having a particle size within a specific range and having a favorable particle form (Patent Document 3)”, while an example of another common method is “the use of an admixture (plasticizer)”. However, these methods have the problem of having a detrimental effect on strength development while also resulting in increased production costs.